C. Capsaicin
Synonyms Axsain; Mioton; Zostrix.
Biological Source It is the pungent principle obtained in the fruit of various species of Capsicum, viz., Capsicum annum L. (Solanaceae) (Chilli, Sweet Peppers, Paprika).
Chemical Structure
(E)-N-[4-Hydroxy-3-methoxyphenyl)-methyl]-8-methyl-6-noenamide. It is phenolic in nature.
Isolation The capsicum fruits are crushed and extracted with either hot acetone or ethanol by using the method of percolation. The solvent i.e., hot acetone or ethanol is evaporated under vacuum.
The residue is extracted once again with successive quantities of warm acetone or ethanol until and unless the marc is completely free from any pungent principles. It contains approximately not less than 8% of capsaicin.
Characteristic Features
1. Capsaicin gives a distinct burning taste even when diluted to the extent of one part in one million parts of water. However, its pungency is destroyed by oxidation.
2. It is obtained as monoclinic, rectangular plates, scales from petroleum ether, having mp 65°C.
3. It has bp 0.01 210-220°C (air-bath temperature).
4. It has uv maximum: 227, 281 nm (€ 7000, 2500).
5. It is freely soluble in ether, benzene, chloroform; slightly soluble in CS2; and practically in soluble in water.
Identification Tests
1. An alcoholic solution of capsaicin gives rise to a distinct bluish green colour upon adding a few drops of FeCl3 solution (0.5% w/v).
2. When capsaicin is dissolved in a few drops of concentrated H2SO4 and a few crystals of sucrose is added, it yields a violet colour after a few hours.
Uses
1. It is used as a topical analgesic.
2. It is often employed as a tool in neurobiological research.
3. It is used in creams to counter neuralgia caused by herpes infections and in other pain-relieving formulations.
Biosynthesis of Capsaicin The aromatic fragment of the capsaicin molecule is derived solely from phenylalanine through chemical entities, viz., ferulic acid and vanillin. The later compound, an aldehyde, is actually the substrate for transamination to yield vanillylamine. However, the acid part of the resulting amide structure is of polypeptide origin having essentially a branched-chain fatty acyl-CoA which is produced by chain extension of isobutyryl-CoA. The aforesaid source of reactions are as given under:
